1. Field of the Invention
The present invention relates to a magnetron type sputtering apparatus for forming a thin film on a substrate.
2. Description of the Related Art
A magnetron type sputtering apparatus has been widely used as a method of forming a thin film such as a transparent conductive film a metal film or an insulating film on a substrate such as a glass substrate. A conventional magnetron type sputtering apparatus is constructed as shown in FIG. 1 and FIG. 2. More specifically, in a pressure resistant vessel 1, a substrate S to be covered with a desired film, a target T opposed to the substrate S under the substrate S, a magnet M disposed under the target T, and an anode A between the target T and the substrate S are disposed. The magnet M is provided to seal a plasma by a magnetic field, and provided with an S pole around an N pole which is laterally long. The anode A is formed in a loop shape of a conductive wire material and disposed to surround the outer periphery of the substrate S.
This sputtering apparatus generates a plasma by supplying a discharge current between a cathode electrode of the target T and the anode A and sputters with the plasma. The plasma is confined in the surface of the target by a magnetic field indicated by lines f of magnetic force of the magnet M. The target T is sputtered by the plasma confined in the magnetic field of the magnet M, and the sputter particles thus sputtered are flown toward the substrate S, and deposited on the surface of the substrate S. As a result, the target T is cut more on the surface in the portion having higher density of the plasma to form an erosion Ta. Since the erosion Ta becomes high in the density of the plasma on the surface of the target corresponding to an intermediate point between the S pole and the N pole of the magnet M, the erosion Ta is formed in a ring shape on the surface of the target T corresponding to the intermediate point between the S pole and the N pole of the magnet M, and deepened as the sputtering time is elapsed. When the sputtering time becomes long so that the depth of the erosion Ta becomes deep to arrive at the lower surface of the target, the target is replaced.
There is also known an in-line type sputtering apparatus for continuously depositing films on a number of substrates to enhance the efficiency of depositing the films as a sputtering apparatus. The in-line type sputtering apparatus is constructed schematically as shown in FIG. 3. More particularly, in a sputtering chamber 10, an inlet chamber 12 is bonded to the front side of the sputtering chamber 10, and an outlet chamber 13 is bonded to the rear side of the sputtering chamber 10 through airtight doors (not shown). A substrate 1S to be formed with a film is mounted on a substrate carrier (not shown), and introduced into the inlet chamber 12. The inlet chamber 12 is reduced under pressure, the airtight door (not shown) is then opened, and the substrate 1S is carried into the sputtering chamber 10, and formed with a film by sputtering while the substrate 1S is moved in the sputtering chamber 10. Then, the airtight door (not shown) is opened, the substrate 1S is carried into a pressure-reduced outlet chamber 13, the outlet chamber 13 is returned to the atmospheric pressure, and the substrate carrier is then delivered.
A heater 14 for heating the substrate 1S carried into the sputtering chamber 10 is provided in the sputtering chamber 10, and a film forming portion 17 is provided at the rear of the heater 14 (at the front of the substrate 1S in the moving direction). The film forming portion 17 is composed of a target 1T opposed to the film forming surface of the substrate 1S moving in the sputtering chamber 10, a magnet (permanent magnet) 1M disposed behind the target 1T for generating a magnetic field for confining a plasma, and an anode 1A made of a conductive metal wire material disposed opposed to the target 1T.
When a metal oxide film such as, for example, an ITO is formed by this sputtering apparatus, argon gas (Ar) and oxygen gas (O.sub.2) are introduced as sputtering gases into the sputtering chamber 10, a sputtering is conducted by the target 1T made of ITO in the sputtering gas atmosphere to form an IT0 on the film forming surface of the substrate 1S. The substrate 1S carried into the sputtering chamber 10 is heated to a predetermined temperature (a temperature capable of forming a film by sputtering) in the step of passing the heater 14 while moving the substrate 1S by a substrate carrier, and formed with a film by sputtering while passing a film forming portion. The sputtering is conducted by supplying a discharge current between a cathode electrode of the target 1T and an anode 1A. A plasma generated by supplying the discharge current is confined in the vicinity of the surface of the target 1T by a magnetic field of the magnet 1M. Sputtering particles sputtered from the target 1T by the plasma are flown toward the substrate 1S, and deposited on the substrate 1S. In the in-line type sputtering apparatus, the target 1T is also cut more, similarly to the above-mentioned sputtering apparatus of FIGS. 1 and 2, on the surface in the higher density of the plasma as the sputtering time is elapsed to form a ring-shaped erosion 1Ta on the surface of the target 1T corresponding to the intermediate point between the S-pole and the N-pole of the magnet 1M. The erosion 1Ta becomes deep as the sputtering time becomes long. When the depth of the erosion 1Ta reaches the lower surface of the target, the target is replaced.
In order to replaced the target, as shown in FIG. 4, an opening 10a is formed at the sidewall of the sputtering chamber 10. The target 1T is attached to the inner surface of an openable door 11 made of a copper plate for sealing the opening, and the door 11 is opened when the target 1T is consumed to its available limit to replace the target 1T.
The magnet 1M is attached to the outer surface of the door 11, and the anode 1A is attached to an anode supporting member 15 provided in the sputtering chamber though an insulating member 16.
The sputtering rates (film depositing efficiency on the substrate S, 1S) of the sputtering apparatuses described above are determined by the discharge current supplied between the target T, 1T and the anode A, 1A. The larger the discharge current is supplied, the higher the sputtering rate becomes.
However, in the conventional sputtering apparatuses described above, there arises a problem that if the discharge current is increased, a discharging state becomes unstable. Therefore, it was difficult to raise the sputtering rate by increasing the discharge current value.
In the conventional sputtering apparatuses described above, the linear anodes A, 1A are disposed to surround the substrates S, 1S. Since a difference in the discharging states occurs above and below the anodes A, 1A and/or at the right and left sides of the peripheries of the anodes A, 1A, the degrees of the progresses of the erosions Ta, 1Ta of the targets T, 1T become irregular as shown in FIG. 1 when the sputtering is repeated. If the erosions Ta, 1Ta of the targets T, 1T are proceeded to the depth arriving at the lower surfaces of the target T, 1T even only at the portions of the targets T, 1T, though the target material having a thickness sufficiently available for use remains under the erosions Ta, 1Ta of the other portion, the targets T, 1T become impossible to be used at this time. Therefore, the above-described conventional sputtering apparatus has a problem in which the utility efficiency of the target A is deteriorated.
In the conventional sputtering apparatuses described above, the target 1T is attached to the inner surface of the openable door 11, and the anode 1A is mounted in the sputtering chamber 10. Therefore, it has a problem that regulation of the position of the anode 1A to the target 1T is very difficult. In other words, in order to regulate the position of the anode 1A to the target 1T, the steps of closing the openable door 11, opposing the target 1T on the inner surface of the openable door 11 to the anode 1A in the sputtering chamber 10, opening the openable door of the sidewall of opposite side to the sputtering chamber 10, checking the position of the anode 1A from the opening of the opposite side, then opening the openable door 11, correcting the position of the anode 1A, again closing the openable door 11, and checking the position of the anode 1A after correction from the opening of the opposite side must be repeated. Accordingly, the above-mentioned conventional sputtering apparatus has a problem that the position regulating work of the anode 1A is very complicated in a low efficiency.
It is an object of the present invention to provide a sputtering apparatus which can solve the above-described problems and produce a stable and uniform discharge state with a large discharge current, thereby enhancing a sputtering rate and forming a film in high efficiency.